Synthesis and release of eicosanoids by fetal membranes in response to fetal or maternal signals may be involved in the onset of parturition in humans. However, the intracellular events occurring in amnion and chorion which trigger this response are ill-defined. Mobilization of arachidonic acid by phospholipase(s) is a key regulatory step in arachidonic acid release and metabolism into oxytocic prostaglandins. A group of phospholipase inhibitory proteins, the lipocortins (now called "annexins"), have been identified and implicated in control of prostaglandin production. These proteins appear to regulate phospholipase activity by binding tightly to phospholipids (in a Ca++ dependent manner), effectively sequestering substrate from phospholipase. We have shown that annexins are present in human intrauterine tissues and that their activity changes with labor. In this proposal, we aim to: 1. Identify the cell types that contain annexins and the intracellular localization of annexins in human amnion and chorion obtained before and after the onset of labor, 2. Quantitate the amount of annexins present in human amnion and chorion before and after the onset of labor to establish changes which occur with labor, 3. Characterize the affinity and specificity of interaction of annexins with membrane phospholipids, particularly the interactions with phosphatidyl ethanolamine and phosphatidyl inositol (which are hydrolyzed during labor to release arachidonic acid), 4. Identify the characteristics of binding to phospholipid, divalent cations, and cytoskeletal proteins, to identify annexins with highest affinity for phosphatidyl inositol and phosphatidyl ethanolamine, and 5. Alter site-specific phosphorylation of annexins in vitro and measure the effect on their activity compared to the characteristics of dephosphorylated annexins (specific aims 3 and 4). This will determine whether annexins qualify as phosphoprotein mediators of a metabolic pathway (control of prostaglandin production), by testing whether they satisfy the criteria proposed by Krebs for control by phosphorylation. Once the biochemical changes which occur in specific annexins in fetal membranes at the onset of labor are identified, the defined changes can be used to evaluate candidate signals for parturition, and to assess the effectiveness of therapeutic interventions at the biochemical level, targeted toward identification of agents which may be useful in prevention of pre-term labor.